Drylands are predicted to become more arid and saline due to increasing global temperature and drought. Although species from the Caatinga, a Brazilian tropical dry forest, are tolerant to these conditions, the capacity for germination to withstand extreme soil temperature and water deficit associated with climate change remains to be quantified. We aimed to evaluate how germination will be affected under future climate change scenarios of limited water and increased temperature. Seeds of three species were germinated at different temperatures and osmotic potentials. Thermal time and hydrotime model parameters were established and thresholds for germination calculated. Germination performance in 2055 was predicted, by combining temperature and osmotic/salt stress thresholds, considering soil temperature and moisture following rainfall events. The most pessimistic climate scenario predicts an increase of 3.9 °C in soil temperature and 30% decrease in rainfall. Under this scenario, soil temperature is never lower than the minimum and seldomly higher than maximum temperature thresholds for germination. As long as the soil moisture (0.139 cm 3 cm 3 ) requirements are met, germination can be achieved in 1 day.According to the base water potential and soil characteristics, the minimum weekly rainfall for germination is estimated to be 17.5 mm. Currently, the required minimum rainfall occurs in 14 weeks of the year but will be reduced to 4 weeks by 2055. This may not be sufficient for seedling recruitment of some species in the natural environment. Thus, in future climate scenarios, rainfall rather than temperature will be extremely limiting for seed germination.
Myracrodruon urundeuva, a native species from the Brazilian Caatinga, is widely distributed across its endemic region, where it also plays an essential socioeconomic role. The objective of this study was to evaluate the influence of environmental stress on the germination of M. urundeuva seeds harvested in different years (2010 to 2013). Seeds were germinated at constant temperatures between 10 to 40 °C, osmotic potentials from 0 to -0.8 MPa (in polyethylene glycol 6000 solutions), and from 0 to -0.5 MPa (in NaCl solutions). The experiment was conducted according to a completely randomized design, with three replicates of 50 seeds, in a factorial scheme (harvest year x stress intensity) for each environmental stress. Germination data were then analysed using thermal, hydro and halo time models, and future germination responses projected according to climate change scenarios. The germination thermal thresholds ranged from 7.4 to 53.3 oC. The germination base osmotic threshold (using polyethylene glycol) was -0.6 MPa and the base osmotic threshold in NaCl was -0.43MPa. Seeds from different harvest years showed distinct tolerance to environmental stresses. The thermal, hydro and halo-time models were efficient to describe the germinative response of seeds, and the climate models allowed to identify the germination responses of M. urundeuva in future climate. According to the models for future climate (RCP 8.5), the reduction of rainfall by 2100 will directly affect seed germination and seedling recruitment of M. urundeuva.
-The production of seeds and seedlings by these species is of utmost importance to prevent a loss of biodiversity of the Caatinga, a unique and exclusively Brazilian biome. Biosaline agriculture is conducted over a range of salinity levels in groundwater and/or in soils. The current study evaluated the application of biosaline agriculture to Anadenanthera macrocarpa, Myracrodruon urundeuva, Aspidosperma pyrifolium and Erythrina velutina by examining the germinative metabolism of seeds subjected to different electrical conductivities (ECs) of NaCl solutions and biosaline water. The seeds were germinated in biosaline water (4.94 dS.m -1) and in NaCl solutions with ECs of 0, 2, 4, 6, 8, 10, 12, 14, 16 and 18 dS.m -1 at 25 °C, 12-h photoperiod. The kinetic variables of germination were assessed, and the seeds and seedlings were assayed for reserve biomolecules, proline content and antioxidant enzyme activity. The seeds were highly tolerant to salinity, with germination-limiting ECs above 12 dS.m -1. Although high EC promoted alterations in seed metabolism that enabled salinity tolerance, seedling production was indicated with ECs no higher than 6 dS.m . These results demonstrated that Caatinga seedling production is viable through biosaline agriculture beucause the groundwater salinity of this region is within the tolerance levels of the seeds. . Embora, alta CE promova alterações no metabolismo sementes, permitindo tolerância à salinidade, a produção de mudas é indicada em CE inferior a 6 dS.m -1 . Assim, a produção de mudas da Caatinga é viável através da agricultura biossalina, pois as águas subterrâneas da região apresentam-se dentro deste nível.Termos de indexação: enzimas antioxidantes, germinação, mobilização de reserva, estresse salino.
ABSTRACT-Biosaline agriculture has been a viable alternative for agricultural production in regions with lack of good quality water. To enable the cultivation of vegetables in high electrical conductivities, seed priming has been used to increase tolerance to stress caused by use of brackish water. We aimed to evaluate the efficiency of osmo and hydropriming in cucumber seeds cv. Caipira germinated biosaline in water, regarding germination and biochemical changes during the germinative process. The experimental design was totally randomized, with four replications of 50 seeds or 10 seedlings, in a factorial scheme 6x3; with six priming conditions (control, osmopriming during 24 and 48 hours, hydropriming with 1, 2 and 3 cycles of hydration-dehydration) and three biosaline water (fish farming biosaline wastewater) concentrations in distilled water (0, 50 e 100%). We evaluated the kinetics and percentage of germination; germinative metabolism and activity of antioxidant enzymes. According to the results, one hydropriming cycle is faster and more efficient to improve the performance of cucumber seedling in biosaline water and this can be used in substrate for germinating seeds of cucumber cv. Caipira.Index terms: water reuse, Curcubitaceae, seedling development.Modificações fisiológicas em sementes de pepino osmo e hidrocondicionadas germinadas em água biossalina RESUMO -A agricultura biossalina tem sido uma alternativa viável para a produção agrícola em regiões com escassez de água de boa qualidade. Para possibilitar o cultivo de hortaliças em condutividades elétricas elevadas, o condicionamento fisiológico de sementes tem sido utilizado para aumentar a tolerância destas ao estresse causado pela utilização de água salobra. Objetivouse avaliar a eficiência do osmo e hidrocondicionamento em sementes de pepino cv. Caipira em água biossalina, quanto à germinação e as modificações bioquímicas durante o processo germinativo. O delineamento foi inteiramente casualizado, com quatro repetições de 50 sementes ou 10 plântulas, em esquema fatorial 6x3; sendo seis condições de condicionamento fisiológico (controle, osmocondicionamento durante 24 e 48 horas; hidrocondicionamento com 1, 2 e 3 ciclos de hidratação e secagem) e três concentrações de água biossalina (água residuária de piscicultura) em água destilada (0, 50 e 100%). Foram avaliados: porcentagem de germinação; crescimento inicial de plântulas; metabolismo germinativo e atividade de enzimas antioxidantes. De acordo com os resultados obtidos pode-se concluir que um ciclo de hidrocondicionamento é mais rápido e eficiente para melhorar o desempenho das plântulas de pepino em água biossalina, que pode ser utilizada no substrato de germinação de sementes de pepino cv. Caipira.Termos para indexação: reuso de água, Curcubitacea, desenvolvimento de plântulas.
A B S T R A C TSunflower is a species with multiple potentialities and its yield can be affected by the presence of soluble salts in the soil, which is common in arid, semi-arid and irrigated regions. The objective of this study was to evaluate the effect of hydropriming as inducer of salinity tolerance in seeds and seedlings of sunflower, hybrid MG305CP. The germination tests were set with four replicates of 50 seeds per treatment, maintained in germinator at 30 ºC for ten days. To simulate salinity, sodium chloride diluted in distilled water was used at electrical conductivities of 0 (control), 4, 8, 12 and 16 dS m -1. On the tenth day, the number of normal seedlings was counted and the length and dry matter of shoots and roots were determined. Seedling fresh matter was used to determine the contents of total chlorophyll, total soluble sugars and proline. The experimental design was completely randomized, in a 2 x 5 factorial scheme (with and without hydropriming and five levels of salinity). Hydroprimed sunflower seeds showed greater vigor expression, with higher number of normal seedlings and faster germination.Hidrocondicionamento como indutor de tolerância à salinidade em sementes de girassol R E S U M O O girassol é uma espécie com múltiplas potencialidades, cuja produtividade pode ser afetada pela presença de sais solúveis no solo, fato comum em regiões áridas, semiáridas e irrigadas. Nesta pesquisa, objetivou-se avaliar o efeito do hidrocondicionamento como indutor de tolerância à salinidade em sementes e plântulas de girassol, híbrido MG305CP. Os testes de germinação foram instalados com quatro repetições de 50 sementes por tratamento, sendo mantidos em germinador a 30 ºC por dez dias. Para simular a salinidade, utilizou-se cloreto de sódio diluído em água destilada nas condutividades elétricas de 0 (controle); 4; 8; 12 e 16 dS m -1. No décimo dia, computou-se o número de plântulas normais, comprimento e massa seca de parte aérea e raiz. A partir da matéria fresca de plântulas foi determinado o teor de clorofila total, açúcar solúveis totais e prolina. O delineamento experimental foi o inteiramente casualizado, em esquema fatorial 2 x 5 (com e sem hidrocondicionamento e cinco níveis de salinidade). As sementes de girassol hidrocondicionadas apresentaram maior expressão de vigor com maior número de plântulas normais e germinação mais rápida.
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